When Does Fall Start? Autumn Equinox Signals Season's Beginning

The weather may still be hot and humid in several regions of the country—but autumn is quickly approaching. The fall equinox, which marks the start of the astronomical season of autumn, will arrive Saturday with promises of pumpkin-flavored treats, changing leaves and the Halloween spirit.

The fall equinox takes place in the Northern Hemisphere each year around September 22 or 23, and can vary depending on when exactly the sun reaches the spot directly above the equator. This year, the autumnal equinox falls on Saturday, September 22, so get out the fall decor and the pumpkin spice latte mix—the season is almost here.

There are two equinox events a year, one in the springtime and one in the fall, and they mark the days of the year that are almost equal in the amount of daylight there is compared with darkness.

During the equinoxes, the sun is as close to directly over the equator as it will ever get due to the fact that the Earth is situated at as little a tilt as it ever is. This is different from the solstices, during which the Earth is either tilted in the direction of the sun (summer in the Northern Hemisphere) or away from the sun (winter in the Northern Hemisphere).

The autumn equinox happens when the Earth is tilted as little as it can be on its axis.National Weather Service

When exactly does fall, the autumnal equinox start?

The equinox happens at a different time depending on exact location. In New York City, the equinox is set to happen at 9:54 p.m. EDT, so on the west coast like in Los Angeles, that would be 6:54 p.m. PDT. While it happens at one time, due to time zones it ends up being a different point in the day all around the world.

In New York, the sun is expected to rise at 6:43 a.m. EDT and set at 6:53 p.m. EDT, making the day almost equal parts night and day there, according to Timeand Date. Those closer to the poles of the planet will likely not see such an equal distribution of light and dark.

The amount of daylight gets shorter each day after the summer solstice happens in June, for the month of September each day has been getting shorter by roughly two minutes and 40 seconds per day. Which explains why the sun sets earlier and earlier the closer it gets to autumn.

While the days get shorter and shorter over the next six weeks or so, the end of Daylight Saving Time in November will help bring back some light at the end of the day. Once the winter solstice occurs in December on the shortest day and longest night of the year, the length of daylight will start getting longer again.

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Horses graze in the pasture of the Pleasant Green Fame October 31, 2005, outside of Lexington, Kentucky, as the trees change colors on an autumn afternoon.Jeff Haynes/AFP/Getty Images